Is this So Costly ?
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Thread: Is this So Costly ?

  1. #1
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    Is this So Costly ?

    Hi,

    There is function like
    MyFunction( T* apElements, int anCount );
    As it can be seen it accepts an array as argument..

    In my code, I have a pointer to array ( MyObject** ),
    and I need to pass this array to the MyFinction...

    If I write like followings in my code, does it becomes a costly operation? I mean, I do de-reference 'a pointer to array' to 'an array'; and the size of array is very large( e.g. 100.000 ); In this case how does 'de-referencing' behave ? Does it dereference all thousands of objects or something else ?

    CMain::OnOk()
    {
    MyObject** pMyObjs;
    // create it...
    // initialize them..
    //...
    MyFunction( *pMyObject, 100000 ); // is this de-referencing costly?
    }

    Thanks...

  2. #2
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    Simple answer: no. Such is the beauty of C++

    Toot
    Some cause happiness wherever they go; others, whenever they go.

  3. #3
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    Could you please explaine what exactly going around ?

  4. #4
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    Re: Is this So Costly ?

    Originally posted by the one I mean, I do de-reference 'a pointer to array' to 'an array'; and the size of array is very large( e.g. 100.000 );
    Not quite. T* as a type is just a pointer to T, it's not an array of T. So you have a T**, which is a pointer to a pointer of T, you dereference it and this will become only a pointer to T.

    So the dereference operation only works on the pointer and hence it is quite fast.
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  5. #5
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    Thanks Yves M...

    I want to be sure about another thing,

    I always use (*) as an array instead of ([]) like the example above.

    ( by saying 'as an array', I mean, I keep starting point of sets... )

    Does this usage holds some risks?
    Last edited by the one; February 4th, 2004 at 07:59 AM.

  6. #6
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    Well, the difference is that with * you can have dynamic arrays at runtime, while you cannot do that with []. The only real danger is that you will have memory leaks or memory overwrites, but that's a common problem for c-style arrays.

    If you are writing in C++, I strongly suggest you have a look at std::vector. A good place to start for this is Gabriel's introduction to vector
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  7. #7
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    That's a great article that I will certainly be advising everyone to read. I absolutely agree: STL is both generic and fantastic, but it does have 2 major drawbacks: the documentation is dreadful, hard to find and hard to read; and the code is incredibly hard to read and debug. But that's the price you pay performance, I guess. Of course, you always have a good source of advice...
    Some cause happiness wherever they go; others, whenever they go.

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